Determination of oxygen concentration is important in various fields such as automotive applications, medical devices, anesthesia monitors, and environmental monitoring. Recently, devices based on the fluorescence quenching of organic molecules have been developed to determine the concentration of oxygen. When exposed to light at an appropriate wavelength, the fluorescent substances absorb energy and are promoted from their ground state energy level (So) into an excited state energy level (S1). Fluorescent molecules are unstable in their excited states and can relax by different competing pathways.
Fluorescence based oxygen sensing elements work on the principle that relaxation of the S1 state can also occur through interaction with a second molecule through fluorescence quenching. Molecular oxygen (O2) is an efficient quencher of fluorescence because of its unusual triplet ground state. Fluorophores used for oxygen sensing include: pyrene and its derivatives, quinoline, decacyclene and its derivatives, phenantrene, erythrosine B, and aluminum 2,9,16,23-tetraphenoxy-29H,31H-phthalocyaninehydroxide. These fluorophores are doped into a polymer matrix such as: silicones, polystyrene, and ethyl cellulose that are selectively permeable to oxygen and adhere to glass.
One difficulty with doping fluorescent molecules into a polymer is that the fluorescent molecule may have poor solubility and may crystallize or aggregate within the polymer matrix upon coating and drying.
It would be useful to provide an oxygen sensor that does not crystallize or aggregate within the polymer matrix upon coating and drying.